Tidal Impact on Quiet-Time Polar Thermosphere Zonal Winds During Northern Winter Sudden Stratospheric Warmings

Abstract

This study primarily examines the variability of zonal winds in the geomagnetic “quiet-time” (AE index < 190 nT; Kp index < 2) thermosphere over Alaska (60–75°N) during the winter months from November 2018 to February 2019, and demonstrates a correlation of the meteor radar observed zonal winds at heights 82–98 km with Scanning Doppler Imager observed zonal wind variability at heights 120 and 250 km during nighttime. Notably, over Alaska following a mid-winter sudden stratosphere warming (SSW) event, the zonal wind magnitudes on tidal timescale (difference between maximum eastward and minimum westward wind values over a 6-hr interval during nighttime) in the thermosphere experience about two-fold increase at observed thermosphere altitudes (98, 120, and 250 km). Additional validation of observational findings comes from SD-WACCM-X model simulations across solar-minimum (2017–2021) winters, including both non-SSW and SSW events (occurring in different winters). The model indicates that the SSW-induced response in zonal wind tidal magnitudes may be indistinguishable from the seasonal trend in late winter, while it is more pronounced when the seasonal variations is minimal during mid-winter months. By tidal diagnostics of zonal winds from meteor radar observations and SD-WACCM-X simulations at polar latitudes, a connection is established between the thermosphere zonal wind variations and the semidiurnal originating in the lower atmosphere following the SSW onset within the altitude range of 90–300 km (i.e., ionosphere-thermosphere region). Additionally, the study highlights the migrating solar semidiurnal tides as a major contributor in the variability in the polar thermosphere region with minor contribution from lunar semidiurnal tides.